A pickproof lock is disclosed in U.S. Pat. No. 5,177,987 to Schlage and includes a rod movably received in the plug, wherein the rod has a notch and the plug and the housing respectively have a passage and a smaller passage which are located in alignment with each other. The ball is movably received in the notch, the passage and the smaller passage. When the rod is moved by pushing the operating member in the inside knob, the ball is therefore pushed by the periphery defining the notch and pressed to move toward the smaller passage and straddles the shear line of the plug and the housing so that even if the correct key is inserted into the keyway of the lock, the plug is not rotated. The shifting of the rod to its initial position to let the ball be removed from the shear line between the plug and the housing can only be achieved by a special tool which belongs to the authorized persons. With this lock, some places such as hotels, room guests who are not welcomed will be prohibited from re-entering rooms even if they have keys.
In order to prevent the operating member in the inside knob from being operated unintentionally, the inventor of the present invention discloses the engagement of the operating member and the actuating tube wherein the operating member has to be operated by a tool and moved along the L-shaped groove in the sleeve in which the actuating tube and the operating member are received so that the operating member will not be operated unintentionally. Furthermore, in order to securely retain the operating member in the actuating tube, a rib extends radially outward from the operating member so as to frictionally engage with the actuating tube.